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slides-11 - #11 Eukaryotic transcription (I) 1.Eukaryotes...

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#11 Eukaryotic transcription (I) 1.Eukaryotes RNA polymerases 2.Eukaryotic promoters 3.Enhancers and silencers Pages 257-265 not covered
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1. Transcription initiates at promoters 2. The structure of key subunits of RNA polymerases are similar in prokaryotes and eukaryotes 3. Regulation of transcription initiation is the most common mechanism of gene expression control 4. Transcription is regulated by cis-acting DNA regulatory sequences and trans-acting transcription factors. The principle of transcription regulation is similar in prokaryotes and eukaryotes
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1. Eukaryotic RNA polymerases 1. Different eukaryotic RNA polymerases can be separated by chromatography, distinguished by their relative sensitivity to α - amanitin, a cyclic peptide found in some poisonous mushrooms. 2. Different RNA polymerases transcribe different genes RNA Polymerase - + ++ RNA polymerase I (RNAPI) for most rRNA genes RNA polymerase II (RNAPII) for all mRNA genes RNA polymerase III (RNAPIII) for tRNA, 5S rRNA, etc Sensitivity to α -amanitin
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Most rRNAs are transcribed in a special region of the nucleus, called nucleolus. mRNAs are transcribed in nucleoplasm Experiment : Separate nucleolus and nucleoplasm Purify RNA polymerase from each fraction, and test activity Results : (a) RNA polymerase II is most abundant in nucleoplasm (transcribe mRNA genes) (b) RNA polymease I is most abundant in nucleolus (transcribe rRNA genes) (a) (b) all nucleolus
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Due to structure differences, three eukaryotic RNA polymerases have different sensitivity to α -amanitin, With RNA Pol I being insensitive and RNA Pol II the most sensitive to α -amanitin.
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RNA polymerases have multiple subunits 1. The 3 RNAP have slightly different subunit composition, each has about 11-15 subunits . 2. The major subunits of eukaryotic RNAPs are structurally and functionally similar to that of the prokaryotic RNAP: RPB3 ( α ), RPB2 ( β ), and RPB1 ( β '). 3. Some common subunits are shared by all three eukaryotic RNAPs.
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Eukaryotic and prokaryotic RNA polymerases have similar structure
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1. The amino acids Ser , Thr , and Tyr can be phosphorylated by hydrolysis of ATP to add a Pi at the OH group. His can also be phosphorylated, especially in prokaryotes. 2. Protein phosphorylation is catalyzed by protein kinase . Protein phosphorylation is reversible, a phosphorylated protein can be dephosphorylated by a protein phosphatase . 3. Protein phosphorylation often changes protein structure and activity, so
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This note was uploaded on 02/20/2009 for the course LS 3 taught by Professor Lin during the Spring '06 term at UCLA.

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slides-11 - #11 Eukaryotic transcription (I) 1.Eukaryotes...

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